Just out of curiosity, would you mind posting what gear you use including file types and bitrates? That can have an effect on "as intended" listening. Using bitrates that are too low can distort the music from the way it was originally intended to be heard.
EQ isn't useless. Everyone hears things differently. I suppose you'd say that the balance feature is useless too because it's not "as intended" even though some people hear things louder on one side than the other.
Crossfeed is awesome. It actually can add to the "original intent" because it presents a more lifelike and speaker-like soundstage to headphones/IEMs/etc. Without it, most of my IEMs/headphones seem to have a flat/2d soundstage. If the "original intent" was to be listened through speakers, then wouldn't crossfeed actually help that when listening with headphones and IEMs?
ReplayGain isn't completely useless. It's nice when I have all my songs being shuffled through, but it's not quite as consistent as I'd hoped. But my ears are really sensitive to volume changes though.
They should, but not all do. Even at that, not all gapless players have true 100% gapless seamless playback that works 100% of the time. With Rockbox, it works perfectly, 100% of the time. This is a make-or-break feature for me, but not everyone cares about it.
interface = too much useless information, hard to read
Then change the theme and make the font size bigger! Reading the manual might help too...
battery life = reduced
It's not reduced all that much in some players. In some players (Clip+, IIRC) it's actually increased.
MPEG / multilingual / games / apps / etc = all useless for a music player
How is all that useless? Useless for you maybe, but not for everyone.
I enjoy playing Chopper and Blackjack.
Check out the Rockbox forums, IRC channel, and updates posted on the front page. Seems like it's working pretty well for them.